This application is based upon and claims benefit of priority of Japanese Patent Application No. 2000-337930 filed on Nov. 6, 2000, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnetic switch of a starter motor for cranking an internal combustion engine, the magnetic switch including an auxiliary relay, upon energization of which a main starter switch is closed to supply power from a battery to the starter motor.
2. Description of Related Art
An example of a magnetic switch of this kind is disclosed in JP-A-8-504913. A main starter switch for supplying battery power to a starter motor and an auxiliary relay that closes the main starter switch upon its energization are disposed in a common contact chamber. The main starter switch is composed of fixed contacts and a movable contact, both made of copper, through which a large amount of starter current is supplied. The movable contact hits the fixed contacts at a considerable speed when closing the starter switch. Therefore, copper dusts are generated by abrasion in operating the switch many times and are scattered in the contact chamber.
The auxiliary relay composed of fixed contacts, a movable contact and a relay coil is disposed in the common contact chamber together with the main starter switch, and moreover, the auxiliary relay is exposed to the main starter switch at the bottom side thereof. The contacts of the auxiliary relay are relatively small because they handle a small amount of current that operates the relay. The copper dusts generated by abrasion of the large contacts of the main starter switch adhere to the auxiliary relay, especially to its contacts. The copper dusts are harmful to insulation in the auxiliary relay and switching operation of the contacts. The copper dusts cause malfunctions of the magnetic switch.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved magnetic switch in which abrasion dusts are prevented from entering into a space where the auxiliary relay is installed.
The magnetic switch of the starter motor is mounted on a starter motor. To start an internal combustion engine, the magnetic switch drives its plunger to establish an mechanical engagement between the starter motor and a ring gear of the engine and to supply power from a battery to the starter motor. The magnet switch includes a main motor switch that supplies the battery power to the starter motor upon closing thereof and an auxiliary relay that brings the motor switch to its open or closed position. The motor switch is closed by a plunger driven by a pull-in coil, and its closed position is maintained by a holding coil.
The motor switch includes a movable contact and fixed contacts that handle a large amount of current to be supplied to the starter motor. The auxiliary relay includes a movable contact, stationary contacts and an auxiliary coil for driving the movable contact. The auxiliary relay only handles a relatively small amount of current. The pull-in coil and the holding coil are coaxially wound on a common bobbin, and the auxiliary coil is placed coaxially with the other two coils. A magnetic core which serves as a common magnetic path is positioned between the auxiliary coil and the other two coils wound on the common bobbin.
To start up the engine, a starter switch is closed. Upon closing the starter switch, the auxiliary relay coil is energized to close the auxiliary relay contacts. Upon closing the auxiliary relay contacts, the pull-in coil is energized and the main motor switch is closed to supply the battery power to the starter motor. At the same time, the starter motor is mechanically engaged with the engine, and thereby the rotational torque of the starter motor is transferred to the engine.
The contacts of the main motor switch that are made of copper and handle a large amount of current generate copper dusts in the course of repeated on-and-off operations. If the main switch and the auxiliary relay are placed in a same space, the auxiliary relay, especially its contacts, are exposed to the copper dusts. The copper dusts cause malfunctions of the magnetic switch during the course of long term use. To prevent the auxiliary relay from being exposed to the copper dusts of the main motor switch, a wall separating the auxiliary relay from the main motor switch is provided. The separating wall can be easily provided at a low cost because it has no complex structure.
The auxiliary relay and especially the contacts thereof are kept free from the copper dusts of the main motor switch. Therefore, the starter motor magnetic switch according to the present invention is able to operate for a long time without malfunctions.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.